The present invention relates to a digital signal recording and reproducing apparatus and method including a digital signal overlapped or joined recording method for recording digital data over or joined to portions of other digital data already stored on a writable disc.
In an ordinary compact disc which is referred to hereafter as a CD, a PCM audio signal having a sampling frequency of 44.1 kHz and the number of quantization bits of 16 is recorded in a predetermined recording format as digital data. A CD player for reproducing a digital signal from such a CD is widely used in consumer applications such as audio equipment dedicated for reproduction.
A study of a disc which has a compatible recording format with the aforementioned CD and which allows digital data to be recorded therein has been making progress in recent years. Such a disc is referred to hereafter as a writable disc. The writable disc category so far includes a type that allows digital data to be recorded only once and a type that allows digital data to be rewritten as is described, for example, at pages 48 to 51 of a collection of manuscripts presented at a 1988 JAS conference.
In order to record digital data in CD recording format, a correction code is first added to the digital data, then interleaving based on a simple delay technique is performed on the digital data and, finally, another correction code is added as is described, for example, in Japanese Patent Application Laid-Open No. 57-4629.
When recording digital data into a writable disc in CD format using the simple delay technique, the following problem is encountered. Assuming that digital data is to be recorded over a portion of other digital data already stored on a writable disc allowing data to be rewritten or that a pause has occurred in the writing of the digital data and subsequently additional digital data is written on the disc so as to be joined with the previous and such writable disc is hereafter referred to as a writable disc and such recording is hereafter referred to as overlapped or joined recording, the start and end points of the overlapped or joined recording between two consecutive recording operations are known as edit points. For example, a recording operation is halted temporarily at a point and then followed by another recording operation starting from the point at which the first recording operation was halted. At an edit point which becomes a boundary between existing and overlapping or joined portions of data, an interleave discrepancy results. When playing back a writable disc which underwent overlapped joined recording, an abnormal sound is reproduced at an edit point due to the interleave discrepancy. Such an abnormal sound causes a problem.
A typical countermeasure known so far is described at pages 90 to 93 of D3, a collection of manuscripts presented in a 1986 JAS conference. This countermeasure was devised for preventing the generation of an abnormal sound due to an interleave discrepancy which is caused by a track jump encountered during, for example, a queue review of a CD player. However, the countermeasure was not devised against an abnormal sound due to an interleave discrepancy which is caused by the overlapped or joined recording.
With the proposed countermeasure, during a period between a time of detection of generation of a track jump in the course of reproduction and a time the interleaving is resolved, reproduction data is obtained by interpolation of recorded data immediately before the detection of the track jump as it is and an error flag is set in order to avoid erroneous correction. In this manner, generation of an abnormal sound as a result of the aforementioned conditions can be suppressed. However, the proposed countermeasure described above is, to the bitter end, devised against generation of abnormal sounds due to interleave discrepancies caused by track jumps. Applying the countermeasure, as it is, to abnormal sounds due to interleave discrepancies caused by overlapped or joined recording of digital data into a writable disc will result in the following problems:
With the proposed countermeasure described above, the detection of a track jump in the course of reproduction allows interleave discrepancies to be detected. However, detection of an interleave discrepancy caused by overlapped or joined recording of digital data into a writable disc, that is, an interleave discrepancy occurring on an edit point boundary must be separately provided. Otherwise, such an interleave discrepancy will remain undetected during reproduction.
Even if such an interleave discrepancy at an edit point can be detected, by merely obtaining reproduction data through interpolation of recorded data immediately before the detection of the interleave discrepancy as it is during a period between a time the interleave discrepancy is detected and a time the interleaving is resolved and setting an error flag for prevention of erroneous correction such as proposed by the countermeasure described above, the quality of the reproduced sound in the proximity of the edit point will inevitably deteriorate.
A CD player could be designed to include a facility for solving all the problems described above. With such a CD player, generation of an abnormal sound due to an interleave discrepancy caused by overlapped or joined recording of a writable disc would be reduced. However, generation of an abnormal sound due to an interleave discrepancy caused by overlapped or joined recording of a writable disc would be reduced only if the writable disc was reproduced using a CD player equipped with such a facility. With a CD player having no such facility, such as the type widely available at the present time, the generation of an abnormal sound remains as it used to be. As a result, the problem is basically unsolved.